Hydrochemical appraisal and sources of contamination in high nitrate aquifer, Saudi Arabia

Abstract

A systematic study was executed in the Wadi Fatimah basin, Saudi Arabia to appraise the hydrochemical processes, contamination sources and water quality using an integrated approach namely geochemical methods, multivariate statistical analyses and water quality indices. In this aquifer, the average value of electrical conductivity and total dissolved solids is 4292 µS/cm and 2747 mg/l, respectively. The predominant hydrochemical facies are CaMgCl followed by NaCl. Further, 76% (hardness), 51% (major ions and NO3−) and 15% (F−) of samples surpassed the World Health Organization-prescribed drinking water limit. The contamination index and drinking water quality index (DWQI) also reveal that 25% and 46% of samples are not appropriate for drinking application. Spatial maps of major ions, total hardness and DWQI depict that water quality is deteriorated from upstream to downstream and extreme values exist in the downstream. Gibbs plots, ionic ratios, Pearson correlation coefficient and principal component analysis justify that groundwater chemistry is predominantly affected by evaporation, evaporite dissolution and ion exchange reactions followed by mineral weathering. High NO3− originates from nitrification, irrigation return flow and wastewater recharge. Groundwater F− is derived from weathering of fluoride minerals and enhanced by evaporation. This study emphasizes that proper treatment is required for groundwater before distribution for various uses in this basin.